1. Field of the Invention
This invention relates to a digital tracker of vehicles such as aircraft or maritime vessels to provide range data to collision and more particularly to provide a limiter of the movement of the track gate that updates range data substantially linearly.
2. Description of the Prior Art
The present invention is concerned with improvements in the logic used in the trackers of the so-called SECANT systems of air borne collision avoidance systems, such systems, with suitable modification being useful also for maritime vessels. Such trackers provide means to servo a gate for tracking a target pulse.
In the SECANT tracker, for example, the track gate position is updated by comparing the target range stored in the range counter with the range stored in the range register. A more complete description of such a system is disclosed in U.S. Pat. No. 3,803,604 entitled "Digital Tracker," issued on Apr. 9, 1974, to B. Case. After the comparison is made, the contents of the range register is updated by plus one or minus one or zero counts depending on the outcome of the comparison. This particular feature of the SECANT-type tracker operation is disclosed in U.S. Pat. No. 3,803,605 entitled "Track Gate Movement Limiter," issued on Apr. 9, 1974, to J. E. Miller and B. Case. The present invention provides a simplification of the logic required to achieve such a comparison to achieve the track gate limiting action.